A hosted application is a software application where the software resides on servers that are accessed through a wide-area network, such as the Internet, rather than more traditional software that is installed on a local server or on individual client computers. Hosted applications may also be known as Internet-applications, application service providers (“ASPs”), web-based applications, or on-line applications. Hosted applications are commonly utilized concurrently by multiple subscriber organizations, called “tenants.”
Some hosted applications utilize a multi-tier architecture wherein the middle-tier that performs the application logic is separated from the database-tier where application and tenant data is stored. In many cases, the database-tier is shared among all of the tenants. Use of a shared database-tier in this manner is problematic, however, because a scheduled or unscheduled database outage in such a system will affect all of the tenants simultaneously. Moreover, because all tenants share the same database-tier, application performance for all of the tenants may be significantly reduced if just one tenant places an excessive load on the database. Reduced performance may be unacceptable to the tenants of such a system. Additionally, when a single database is utilized for all of the tenants of a hosted application, it may be difficult for a tenant to customize the schema that is utilized to store the database.
Other hosted applications utilize a multi-tier architecture wherein each tenant utilizes a middle-tier and a database-tier that are maintained separately from all other tenants. This type of architecture may be implemented, for instance, by providing each tenant with a virtual server computer for hosting the middle-tier and the database-tier. This type of architecture allows outages to be confined to a single tenant or a small group of tenants, and reduces the possibility that an excessive load by one tenant will impact application performance for other tenants. This type of architecture, however, suffers from several other significant drawbacks. In particular, it can be complex and expensive to operationally maintain the separate operating system and application installation on the virtual server computer provided for each hosted tenant. Moreover, allocated hardware resources may remain unused by tenants that cannot utilize all of the processing and storage capabilities of a dedicated virtual server computer.
Hosted multi-tenant applications implemented using previous architectures also suffer from several other limitations. In particular, it may be very difficult to add additional hardware capacity to these systems or to upgrade software components without causing downtime for the tenants. Additionally, it may also be difficult to geographically distribute the processing and data storage capabilities of systems that are implemented using these previous architectures.
It is with respect to these considerations and others that the disclosure made herein is provided.